True Color Image By Modified Microlens Array

ABSTRACT

An image sensor array includes a substrate having at least three image sensors located therein. The image sensor array also includes a blue filter positioned proximate to the first image sensor; a green filter proximate to the second image sensor; and a red filter proximate to the third image sensor. A first microlens is positionally arranged with the blue filter and the first image sensor; a second microlens is positionally arranged with the green filter and the second image sensor; and a third microlens is positionally arranged with the red filter and the third image sensor. The first microlens has a larger effective area than the second microlens, and the second microlens has a larger effective area than the third microlens.

CROSS REFERENCE

This application is a Continuation of U.S. patent application Ser. No.11/330,481, filed Jan. 12, 2006, the disclosure of which is incorporatedherein by reference.

BACKGROUND

The present disclosure relates generally to image sensor arrays and,more specifically, to an image sensor array utilizing a modifiedmicrolens array.

Image sensor arrays widely employ in various technologies, includingcharged coupling device (CCD) image sensors and complimentarymetal-oxide-semiconductor (CMOS) image sensors. In general, CCD, CMOS,and other types of image sensor arrays transform a light pattern (i.e.,an image) into an electric charge pattern. Image sensor arrays generallyinclude polymer or dielectric microlenses. The microlenses are oftenarranged in a microlens array, with each microlens in the array beingsimilarly sized and shaped.

In many applications, a selection of wavelengths/colors is received bythe image sensor array. For example, red, green, and blue pixels(filtered image sensor elements) are often used in many imaging systemssuch as a digital camera. It is noted that different photo responsesensitivities exist between the different colored pixels. This isinherently the case due to the different wavelengths of the differentcolors. In continuation of the present example, one pixel's sensitivityto blue light is less than another pixel's sensitivity to green light,which is less than yet another pixel's sensitivity to red light. It isdesired to have these sensitivities (for blue, green, and red, in thepresent example) similar each other, thereby obtaining a more “truecolor” image.

Accordingly, what is needed in the art is an improved image sensorarray, pixel, and method of creating same.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a cross sectional view of a lithography system used forcreating an image sensor array.

FIGS. 1 and 2 provide cross-sectional views of an image sensor array.

FIG. 3 provides a top view of a mask for use in the lithography systemof FIG. 1.

FIGS. 4 and 5 are graphs of a photo response of various image sensorarrays, including the image sensor arrays of FIGS. 1 and 2.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, of systems and methods benefitingfrom aspects of the present invention. Specific examples of componentsand arrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. In addition, the present disclosure may repeat referencenumerals and/or letters in the various examples. This repetition is forthe purpose of simplicity and clarity and does not in itself dictate arelationship between the various embodiments and/or configurationsdiscussed. Moreover, the formation of a first feature over or on asecond feature in the description that follows may include embodimentsin which the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

Referring to FIG. 1, one embodiment of a semiconductor chip 100 includesa substrate 110 and image sensors 120 formed therein. In the presentembodiment, the substrate 110 is a silicon substrate, but in otherembodiments the substrate may comprise such things as germanium ordiamond. It is understood that front-side and back-side illuminationimage sensors can benefit from the present invention, with the substrate110 appropriately configured. For the sake of further example,front-side illumination configuration will be further described.

The substrate 110 may also comprise a compound semiconductor such assilicon carbide, gallium arsenic, indium arsenide, and/or indiumphosphide. The substrate 110 may comprise an alloy semiconductor such assilicon germanium, silicon germanium carbide, gallium arsenic phosphide,and/or gallium indium phosphide. The substrate 110 may include anepitaxial layer. For example, the substrate may have an epitaxial layeroverlying a bulk semiconductor. Further, the substrate may be strainedfor performance enhancement. For example, the epitaxial layer maycomprise semiconductor materials different from those of the bulksemiconductor such as a layer of silicon germanium overlying a bulksilicon, or a layer of silicon overlying a bulk silicon germanium formedby a process such as selective epitaxial growth (SEG). Furthermore, thesubstrate 110 may comprise a semiconductor-on-insulator (SOI) structure.For example, the substrate may include a buried oxide (BOX) layer formedby a process such as separation by implanted oxygen (SIMOX). Thesubstrate 110 may comprise a p-type doped region and/or an n-type dopedregion. The doping may be implemented by a process such as ionimplantation. The substrate 110 may comprise lateral isolation featuresto separate different devices formed on the substrate. In the presentembodiment, the image sensors 120 are photodiodes diffused or otherwiseformed in the substrate 110 and separated by shallow trench isolation(STI) regions 125.

Aspects of the present disclosure are applicable and/or readilyadaptable to image sensor arrays employing various types of devices,including charged coupling device (CCD) and complimentarymetal-oxide-semiconductor (CMOS) image sensor applications (e.g.,active-pixel sensors), among others. As such, the image sensors 120 maycomprise conventional and/or future-developed image sensing devices.

The semiconductor chip 100 includes a passivation layer 130. Thepassivation layer 130 may comprise silicon nitride (e.g., Si₃N₄),silicon oxynitride (e.g., Si_(x)N_(y)O_(z)), silicon oxide, silicondioxide, and/or other materials. The passivation layer 130 may besubstantially optically transparent, and may be formed by chemical vapordeposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), spin-on coating, and/or other processes. In oneembodiment, the passivation layer 130 has a thickness ranging betweenabout 1 μm and about 50 μm. The passivation layer 130 may furthercomprise a multilayer interconnect structure formed therein. Themultilayer interconnect may include metal lines for lateral connectionsand via/contact features for vertical connections. The metal lines andvia/contact features may be configured such that the image sensors 120may not be blocked thereby from incident light. The passivation layer130 may have a multilayer structure such as a layer having themultilayer interconnects embedded therein and a layer to protect theunderlying interconnects and the substrate.

The semiconductor chip 100 includes a dielectric layer 140. Thedielectric layer 140 may comprise silicon nitride, silicon oxynitride,silicon oxide, silicon dioxide, and/or other materials. The dielectriclayer 140 may also comprise a low-k dielectric layer having a dielectricconstant less than or equal to about 3.9. The dielectric layer 140 maybe formed by CVD, PVD, ALD, spin-on coating, and/or other processes. Infurtherance of the present embodiment, the dielectric layer 140 includesa multilayer structure including a planarization layer, a color filterlayer, and/or a spacer layer. The dielectric layer 140 may be formed bya method described above and may be substantially planar, possibly theresult of chemical-mechanical-polishing (CMP). Different color filtersmay be positioned such that the incident light is directed thereon andthere through. In one embodiment, such color-transparent layers maycomprise a polymeric material (e.g., negative photoresist based on anacrylic polymer) or resin. The color filter layer may comprise negativephotoresist based on an acrylic polymer including color pigments. Thespacer layer is formed to adjust the distance between the overlyingmicrolens array and the underlying image sensors 120. In one embodiment,the dielectric layer 140 has a thickness ranging between about 0.2 μmand about 50 μm.

A layer of photoresist 150 is formed over the semiconductor chip 100using a method such as spin-on coating. The layer of photoresist 150 maybe pre-baked. The photoresist layer may then be exposed to a lightsource 300 through a photomask 200, wherein the photomask 200 isspecially designed according to the present disclosure. It is understoodthat in the present embodiment, microlenses are formed from thephotoresist 150. In other embodiments, one or more intermediate layerscan be provided and patterned by the photoresist 150, and these layer(s)can be used to form the microlenses.

Referring to FIG. 2, three different microlenses are formed, designatedwith the reference numeral 155 r (for red), 155 g (for green), and 155 b(for blue). It is understood that the drawings and present disclosureare simplified to better illustrate the various embodiments of thepresent invention. As shown in the figure, the three microlenses(collectively referenced 155) have different effective areas, in thefollowing order:

-   -   effective area of microlens 155 b>microlens 155 g>microlens        155 r. Also, in the present embodiment, there is a gap 160        between the red microlens 155 r and the green microlens 155 g,        and there is no gap 165 between the green microlens 155 g and        the blue microlens 155 b. The gap 160 may prevent portions of        the incident light from being accurately directed toward the        underlying image sensor 120. Various techniques can be used to        obtain the different sized microlenses 155, as discussed in        greater detail below.

Referring to FIG. 3, in one embodiment, optical proximity correction(OPC) is applied to the mask 200 to make changes in the respectivegeometries of the microlenses 155. In the present example, the mask 200is shown having four areas identified as B, G1, G2, and R, whichcorrespond to blue, green, green, and red pixels on the substrate 100(FIGS. 1-2). Correspondingly, microlens images 205, 210, 215, and 220are provided to in the areas B, G1, G2, and R, respectively. Themicrolens images 205, 210, and 220 also correspond to the microlenses155 b, 155 g, and 155 r, respectively, of FIG. 2.

Referring also to FIG. 4, using OPC, features can be applied to one ormore of the mask microlens images 205-220 to produce desired alterationsto the microlenses 155. The vertical axis shows a photo response. Thehorizontal axis shows the wavelength of the light being provided to thevarious pixels, including a blue band 405, a green band 410, and a redband 420. For the sake of comparison, two conventional photo responsesare shown, a first response 430 for a standard pixel elementcorresponding to the wavelength, and a second response 440 for a thinbackend (backside illuminated) pixel element corresponding to thewavelength. As can be seen, the photo response for the variouswavelengths are such that:

-   -   blue 405<green 410<red 420.

Referring again to FIG. 3, OPC features are applied to increase the sizeof the blue microlens image 205 in a direction towards the greenmicrolens images 210 and 215. In the drawing of FIG. 3, the features aregraphically represented as a larger dotted box. It is understood thatdifferent features, or different shaped features, can be used for OPC,as is well known in the art and as dependent on the photolithographyequipment being used. As a result, the corresponding microlenses arecloser to each other. For example, in FIG. 2, the microlenses 155 b, 155g are next to each other without a gap 165 therebetween. Similarly, OPCfeatures (or the lack thereof) are applied to decrease the size of thered microlens image 220 in a direction away from the green microlensimages 210 and 215. As a result, the corresponding microlenses arefurther from each other. Referring again to the example in FIG. 2, themicrolenses 155 g, 155 r have a gap 160 therebetween. It is understoodthat various degrees of OPC can be applied to produce different amountsof gaps (or lack thereof) to achieve a desired result.

Referring again to FIG. 4, in the present example, a resulting photoresponse 450 is provided by the modified microlens images 205-220 of themask 200. As can be seen, the photo response at the blue wavelength 405is improved, and is closer to that of the photo response at the greenwavelength 410 and red wavelength 420.

Referring now to FIG. 5, in another embodiment, the layout of microlensimages 205, 210, 215, and 220 (FIG. 3) are specifically modified in sizeand shape to accommodate for the differences in photo responses 405,410, and 420. Specifically, a ratio of the photo responses forblue:green:red is measured to be about 5:8:12, as shown by the firstresponse 430. It is understood that a different ratio may be obtainedfor the second response 440 or other response, as so determined.Accordingly, the size ratio of the blue microlens image 205: greenmicrolens image 210, 215: red microlens image 220 is also set to 5:8:12.As a result, a near-linear photo response 460 is provided across all ofthe pixel elements.

Thus, several different embodiments have been shown for implementingdifferent features of the present invention. In one embodiment, a methodis provided for making an image sensor array. The method includesproviding a substrate having first and second image sensors locatedtherein and forming first and second filters proximate to the first andsecond image sensors, respectively. First and second microlenses areformed proximate to the first and second filters, respectively, suchthat the first microlens has a larger effective area than the secondmicrolens.

In some embodiments, the method further includes providing the substratewith a third image sensor located therein and forming a third filterproximate to the third image sensor. A third microlens is formedproximate to the third filter, such that the second microlens has alarger effective area than the third microlens.

In some embodiments, the first, second and third filters are configuredto transmit blue, green, and red light, respectively.

In some embodiments, the steps of forming the three microlenses includeutilizing a mask with different sized first, second and third areascorresponding to the first, second, and third microlenses, respectively.In some embodiments, at least one of the steps of forming the threemicrolenses includes utilizing optical proximity correction differentlyon first, second and third mask areas corresponding to the first,second, and third microlenses, respectively.

In another embodiment of the present invention, an image sensor array isprovided. The image sensor array includes a substrate having a pluralityof image sensors located therein and a microlens layer. The microlenslayer includes a plurality of microlenses located over the substrate,each of the plurality of microlenses including a substantially convexportion substantially aligned over a corresponding one of the pluralityof image sensors. At least two of the microlenses of the microlens layerhave different effective areas.

In another embodiment of the present invention, an image sensor array isprovided. The image sensor array includes a substrate having at leastthree image sensors located therein. The image sensor array alsoincludes a blue filter positioned proximate to the first image sensor; agreen filter proximate to the second image sensor; and a red filterproximate to the third image sensor A first microlens is positionallyarranged with the blue filter and the first image sensor; a secondmicrolens is positionally arranged with the green filter and the secondimage sensor; and a third microlens is positionally arranged with thered filter and the third image sensor. The first microlens has a largereffective area than the second microlens, and the second microlens has alarger effective area than the third microlens.

In some embodiments, the three microlenses are formed utilizing a maskwith different sized first, second and third areas corresponding to thefirst, second, and third microlenses, respectively.

In some embodiments, the three microlenses are formed utilizing opticalproximity correction differently on at least one of the first, secondand third mask areas corresponding to the first, second, and thirdmicrolenses, respectively.

In some embodiments, there is a gap between the second and thirdmicrolenses and no gap between the first and second microlenses.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein. Forexample, the microlenses 155 g, 155 r, 155 b are differently sized, ascompared to each other, by using an advance ridge structure, as isdisclosed in U.S. Ser. No. 11/064,452, which is hereby incorporated byreference. Those skilled in the art should also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions and alterations herein without departing from the spiritand scope of the present disclosure.

1. An image sensor array, comprising: a substrate having a plurality ofimage sensors located therein; and a microlens layer comprising at leasta first, second, and third microlens located over the substrate, each ofthe plurality of microlenses including a convex portion aligned over acorresponding one of the plurality of image sensors, wherein the first,second, and third microlenses of the microlens layer have differenteffective areas, wherein the first and second microlenses are adjacenteach other, and wherein the second microlens is next to the thirdmicrolenses and there is a gap between the second and third microlenses.2. The image sensor array of claim 1 further comprising a plurality offilters located between the microlens layer and the image sensors, eachof the filters being aligned between an individual microlens and anindividual image sensor.
 3. The image sensor array of claim 2 wherein atleast two microlenses are configured by at least two different maskimages, and wherein at least one of the mask images includes opticalproximity correction.
 4. The image sensor array of claim 2 wherein theat least two microlenses are configured by at least two different shapedmask images.
 5. An image sensor array, comprising: a substrate having atleast three image sensors located therein; a blue filter positionedproximate to the first image sensor, a green filter proximate to thesecond image sensor, and a red filter proximate to the third imagesensor; a first microlens positionally arranged with the blue filter andthe first image sensor, a second microlens positionally arranged withthe green filter and the second image sensor, and a third microlenspositionally arranged with the red filter and the third image sensor;wherein the first microlens has a larger effective area than the secondmicrolens, and the second microlens has a larger effective area than thethird microlens.
 6. The image sensor array of claim 5 wherein the threemicrolenses are formed utilizing a mask with different sized first,second and third areas images corresponding to the first, second, andthird microlenses, respectively.
 7. The image sensor array of claim 6wherein wherein at least one of the mask images include opticalproximity correction.
 8. The image sensor array of claim 5 wherein thefirst and second microlenses are closely adjacent each other, and thereis a gap between the second and third microlenses.
 9. The image sensorarray of claim 8 wherein there is no gap between the first and secondmicrolenses.
 10. The image sensor array of claim 5 wherein the threeimage sensors are configured to receive front-side illumination.
 11. Theimage sensor array of claim 5 wherein the first, second, and thirdmicrolenses have a size ratio of approximately 12:8:5.
 12. The imagesensor array of claim 5 wherein the second image sensor is a nextadjacent image sensor to the first image sensor, and the third imagesensor is the next adjacent image sensor to at least one of the firstimage sensor and the second image sensor.
 13. An image sensor array,comprising: a substrate having at least three image sensors locatedtherein; a first color filter positioned proximate to the first imagesensor, a second color filter proximate to the second image sensor, anda third color filter proximate to the third image sensor; a firstmicrolens positionally arranged with the first color filter and thefirst image sensor, a second microlens positionally arranged with thesecond color filter and the second image sensor, and a third microlenspositionally arranged with the third color filter and the third imagesensor, wherein the first and second microlenses are closely adjacenteach other, wherein the second microlens is next to the third microlens,wherein there is a gap between the second and third microlenses, andwherein the gap is defined using optical proximity correction.
 14. Theimage sensor array of claim 13 wherein the first, second, and thirdmicrolens have a first, second and third effective area respectively,wherein the first effective area is determined by a ratio of a photoresponse of the first image sensor when aligned with the first colorfilter, wherein the second effective area is determined by a ratio of aphoto response of the second image sensor when aligned with the secondcolor filter, wherein the third effective area is determined by a ratioof a photo response of the third image sensor when aligned with thethird color filter, wherein the image sensor array has approximatelyequivalent sensitivities to the light filtered through each of thefirst, second, and third color filters.
 15. The image sensor array ofclaim 14 wherein there is no gap between the first and secondmicrolenses.
 16. The image sensor array of claim 13 wherein the threemicrolenses are formed utilizing a mask with independently sized first,second and third images corresponding to the first, second, and thirdmicrolenses, respectively.
 17. The image sensor array of claim 13wherein the first, second, and third filters are configured to transmitblue, green, and red light, respectively.
 18. The image sensor array ofclaim 17 wherein the first microlens has a larger effective area thanthe second microlens, and the second microlens has a larger effectivearea than the third microlens.
 19. The image sensor array of claim 18wherein the first, second, and third microlenses have a size ratio ofapproximately 12:8:5.
 20. The image sensor array of claim 16 wherein atleast one of the mask images include optical proximity correction.